Dancing is the DX/A skill of performing dances appropriate to your culture. It defaults to DX-5, and people who know the skill are able to learn new dances quickly, apparently acquiring familiarity after doing a dance three times, rather than needing a day's worth of practice. Dancing takes Cultural Familiarity modifiers, and seems to be the only DX-based skill that does so. Exotic dances (Bull-dancing, fire dancing, snake dancing) can be separate DX/A skills defaulting to Dancing-5 at the GM's discretion.
I suspect that many kinds of popular dance are have substantial skill bonuses, and anyone with points in the skill is a "good dancer" by the standards of the general population. Professionals, naturally, will have substantial training. Group Performance (Choreography) has a prerequisite of Dancing, and defaults to Dancing-2.
Dancing is a worthwhile social skill for "Face" characters, and a lifeline for high-DX low-IQ characters who have to operate in high society. It's a common entertainment and social activity in most human societies and important in some religions' rituals.
Dancing is a common background skill on templates, but rarely compulsory. There are a few templates and archetypes that have it as a primary skill, such as the Wardancer in
Fantasy, who is mostly an entertainer, and Shamans in
Lands Out of Time.
Madness Dossier Irruptors can use it for Enthrallment, because they can use anything that allows communication, and
LTC1 points out its usefulness in attaining trance states.
Martial Arts has Dancing Feints and other ways to use it in a style, which
Yrth Fighting Styles builds on.
Social Engineering has it as a substitute influence skill, and a complementary skill to influence skills.
PU2: Talents and
PU7: Wildcard Skills have examples that include Dancing.
I've played a scenario recently where Dancing was important, since one had to reproduce a sacred dance to get past a magical barrier. I also have a character who, thanks to
Dr Kromm, uses Dancing for movement in tight quarters without bumping into people - it's a good way of sneaking through doors while you're invisible.
What have you done with Dancing in a game?